The present invention is directed to dual-axis magnetometers. It finds particular application where miniaturization is desired.
Numerous applications require accurate determination of the orientation of an object with respect to a magnetic field. The magnetic field of the earth is often of interest, for example, both in navigation and in other applications requiring orientation sensing.
An example of an application in which the magnetic field of the earth is sensed in order to determine orientation is the use of a magnetometer to detect the orientation of an acoustic array that is deployed in the ocean in order to form precise acoustical beam patterns. In this type of application, dual-axis magnetometers can be employed. Specifically, if the direction and inclination of the earth's magnetic field at the location of the array are known, it is possible to determine the orientation of the array, and the directions of the beams formed by it, through the use of two orthogonally oriented dual-axis magnetometers that provide the orientation of the array relative to the earth's field. Alternatively, a gravitational sensor can be used in conjunction with a single dual-axis magnetometer to determine orientation.
Dual-axis magnetometers have been realized in the past by employing flux gates. However, employment of the flux gate in orientation sensors of the type described above has certain disadvantages. While relatively small flux gates have been described in the literature, those commercially available tend to be rather large. Furthermore, they present design problems because of their sensitivity to temperature. In addition, there is a tendency for them to interfere with other magnetic instrumentation. In sensing of acoustic-array orientation, on the other hand, it is important that the orientation sensor be small so as to minimize flow noise during towing of the arrays, and it is desirable that the device be simple and inexpensive to manufacture so that it can be used with expendable acoustic-array systems.
It is accordingly an object of the present invention to provide dual-axis magnetic direction sensing in a device that lends itself to miniaturization and provides sensitive direction detection with a minimum of sensitivity to temperature variation.